EP1004858A1 - Filling level gauge - Google Patents

Abstract

The filling level measuring device includes a receiving- and evaluation switch (15), which receives the reflected signals, determines the running time of the signal as well as the running time in the filling level. Filling level measuring device for measuring filling stand of a liquid (1) in a container (3), has (a) an electronic switch (13) which in operation produces electromagnetic signals; (b) a conductor (7) which protrudes into the container (3), runs the length of the filling level using a float (11,11a,11b,11c,11d,11e) and has at least one electromagnetic signal reflecting part; (c) a coupling (9) which transfers the signal from the switch (13) onto the conductor (7), the conductor feeds signals into the container and removes a reflected signal on the float (11); and (d) a receiving and evaluation switch.

Description

The invention relates to a level measuring device for measurement a level of a liquid in a container the electromagnetic signals towards the Product surface is sent and the echo is received. A transit time is determined which is a signal for the route to the product surface and back and from that the Level determined.

Working with electromagnetic signals Level meters are used in a variety of applications, both in warehousing and in manufacturing Industry, e.g. in chemistry, in the food industry and can be used in the oil industry.

Among others, they work with microwaves Level gauges commercially available. These devices are divided into two classes; a first class, where the microwaves are directed in the direction of an antenna of the product, reflected on the product surface and then after a distance-dependent runtime be received again and a second class in which the Microwaves along a waveguide in the direction of the Fill goods are guided, due to the surface of the product of the impedance jump existing there are reflected and the reflected waves along the waveguide out of the container.

Both a single and a waveguide can be used two or more conductors arranged parallel to each other serve that go from a point above the highest to measuring level down into the container extend.

• eine elektronische Schaltung,

-- die im Betrieb elektromagnetische Signale erzeugt,

• einen Leiter,

-- der in den Behälter hinein ragt,

• eine Einkopplung,

-- die die Signale von der Schaltung auf den Leiter überträgt,

--- welcher Leiter die Signale in den Behälter hinein und an einer Oberfläche des Füllguts reflektierte Signale heraus führt, und

• eine Empfangs- und Auswerteschaltung,

-- die reflektierte Signale empfängt,

-- die eine Laufzeit der elektromagnetischen Signale bestimmt und

-- die aus der Laufzeit den Füllstand ermittelt.

DE-U 94 21 870 discloses a level measuring device for measuring a level of a liquid in a container, which comprises

• an electronic circuit,

- which generates electromagnetic signals during operation,

• a leader,

- that protrudes into the container,

• a coupling,

- which transmits the signals from the circuit to the conductor,

--- which conductor leads the signals into the container and out signals reflected on a surface of the filling material, and

• a reception and evaluation circuit,

- which receives reflected signals,

- which determines the duration of the electromagnetic signals and

- which determines the level from the runtime.

An electronic circuit for generating the electromagnetic signals and a receive and Evaluation circuit is e.g. described in EP-A 780 665.

In the level measuring device according to DE-U 94 21 870 the signals are short electromagnetic impulses at the Surface of the product to be reflected. The share of Signals that are reflected depend on the Difference in dielectric constant from the product and the medium above the product.

If the difference is large, the measurement effect is also clear and the runtime can be determined perfectly. Is the Difference, however, small, so that of the Reflection originating from the product surface is no longer without further be determined. In such applications the level meter described is not functional.

An example of such a problematic application is the measurement of a level in an oil-filled Container. Oil has a dielectric constant of about 2, the air typically above the oil Dielectric constant of 1.

This effect also occurs when using level measurement free microwaves on towards the surface of the Filled goods sent, reflected on the surface and their Echo signal is evaluated to determine the level.

In DE-A 44 19 462 is a working with microwaves Level measuring device described in which microwaves in one into a container protruding still pipe sent become. The surge pipe serves as a waveguide for the Microwaves. It is specified for applications where the product has a low dielectric constant has a float with a highly reflective To provide surface in the surge pipe.

A stillpipe represents a large bulky and therefore unwieldy component and can therefore not be used if there is little space and / or one for an opening provided for a level meter has a small diameter. The installation of a Stillpipe is complex and expensive. Furthermore, e.g. in applications where the stillpipe with viscous and / or sticky media is in contact regular cleaning may be necessary to ensure that the Float remains free to move.

It is an object of the invention to provide a level meter for measuring the level of a liquid in a Container with the electromagnetic signals in the direction of Product surface is sent and the echo is received indicate that liquids with low Dielectric constant measures properly and its Installation and maintenance is simple and inexpensive.

• eine elektronische Schaltung,

-- die im Betrieb elektromagnetische Signale erzeugt,

• einen Leiter,

-- der in den Behälter hinein ragt,

-- entlang dem ein Schwimmer mit dem Füllstand mit läuft,

--- der mindestens ein elektromagnetische Signale reflektierendes Teilstück aufweist,

• eine Einkopplung,

-- die die Signale von der Schaltung auf den Leiter überträgt,

--- welcher Leiter die Signale in den Behälter hinein und ein an dem Schwimmer reflektiertes Signal heraus führt, und

• eine Empfangs- und Auswerteschaltung,

-- die das reflektierte Signal empfängt,

-- die eine Laufzeit der elektromagnetischen Signale bestimmt und

-- die aus der Laufzeit den Füllstand ermittelt.

For this purpose, the invention consists in a level measuring device for measuring a level of a liquid in a container, which comprises

• an electronic circuit,

- which generates electromagnetic signals during operation,

• a leader,

- that protrudes into the container,

- along which a float runs with the level,

--- which has at least one section reflecting electromagnetic signals,

• a coupling,

- which transmits the signals from the circuit to the conductor,

--- which conductor leads the signals into the tank and out of a signal reflected by the float, and

• a reception and evaluation circuit,

- which receives the reflected signal,

- which determines the duration of the electromagnetic signals and

- which determines the level from the runtime.

According to one embodiment, the float is a hollow body and the electromagnetic wave reflecting portion is a metallic or metallic coated Shell surface of the hollow body.

According to one embodiment, the section is one inside electromagnetic signals arranged by the float reflective surface.

According to one embodiment, the section is a vertical one electromagnetic to an axis of the conductor Surface reflecting signals.

According to one embodiment, the float consists of a Material with a high dielectric constant, that reflecting electromagnetic waves.

According to one embodiment, the coupling is on one opposite end of the conductor provided a holder which the swimmer lies on when the Liquid surface is located below the bracket.

According to one embodiment, the float surrounds you cylindrical section of the conductor on all sides.

According to one embodiment, the reflective Section on a reflective surface that matches the Product surface lies in one plane.

Such a level meter offers the advantage that also for liquids with low dielectric constants reliable measurements are possible.

Fig. 1

zeigt eine schematische Darstellung eines ersten Ausführungsbeispiels eines erfindungsgemäßen Füllstandsmeßgeräts in einem Behälter;

Fig. 2

zeigt ein zweites Ausführungsbeispiel eines Füllstandsmeßgeräts;

Fig. 3

zeigt ein drittes Ausführungsbeispiel eines Füllstandsmeßgeräts;

Fig. 4

zeigt ein viertes Ausführungsbeispiel eines Füllstandsmeßgeräts;

Fig. 5

zeigt ein fünftes Ausführungsbeispiel eines Füllstandsmeßgeräts; und

Fig. 6

zeigt ein sechstes Ausführungsbeispiel eines Füllstandsmeßgeräts;

Fig. 7

zeigt eine Elektronik und eine Empfangs- und Auswerteschaltung von Fig. 1; und

Fig. 8

zeigt Meßsignalverläufe eines Füllstandsmeßgeräts mit und ohne Schwimmer.

The invention and further advantages will now be explained in more detail with reference to the figures of the drawing, in which six exemplary embodiments are shown; Identical elements are provided with the same reference symbols in the figures.

Fig. 1

shows a schematic representation of a first embodiment of a fill level measuring device according to the invention in a container;

Fig. 2

shows a second embodiment of a level meter;

Fig. 3

shows a third embodiment of a level measuring device;

Fig. 4

shows a fourth embodiment of a level meter;

Fig. 5

shows a fifth embodiment of a level measuring device; and

Fig. 6

shows a sixth embodiment of a level meter;

Fig. 7

shows an electronics and a receiving and evaluation circuit of Fig. 1; and

Fig. 8

shows measurement signal curves of a level measuring device with and without float.

In Fig. 1 is a first embodiment of a Level meter according to the invention shown. It serves for measuring a level of a liquid 1 in a Tray 3.

The fill level measuring device comprises an outside of the container 3 arranged housing 5 to which a conductor 7 is connected, which protrudes into the container 3. It's one with that Housing 5 connected coupling 9 provided, as in Fig. 1 is only shown schematically in one Opening of the container 3 is mounted. The coupling 9 can e.g. have an external thread, by means of which they in an internal thread arranged in the opening can be screwed in or it may have a flange that is on a the opening surrounding the counter flange can be fastened. Other Types of fastening known to the person skilled in the art are also conceivable.

The conductor 7 is inside the coupling 9 from the housing 5 led into the container 3. The conductor 7 is e.g. on mechanically rigid rod or a mechanically rigid wire. A tensioned rope can also be used in the same way, one end of the housing 5 or the coupling 9 and the other end of which is attached to a bottom of the container is. Instead of attaching the other end to the Container bottom can also have a weight at the other end be attached, through which the rope is tensioned.

On the head 7, a float 11 is provided, which on the liquid floats and thus with the level in the Container 3 runs along. The fill level is in FIG. 1 represented schematically by wavy lines.

An electronic circuit 13 is provided which in Operation generates electromagnetic signals S. These signals S are from the circuit 13 via the coupling 9 transfer the conductor 7 and along the conductor 7 in the Container 3 led into it.

The float 11 has at least one electromagnetic Signals reflecting section in which a share of the signal S is reflected. One on the float 11 reflected signal R is via the conductor 7 from the Container 3 led out.

The reflected signal R is a receive and Evaluated circuit 15, which receives this one Runtime of the electromagnetic signal S from Electronics 13 to the float 11 and the reflected Signal R from the float 11 to the receiving and Evaluation circuit 15 determines and from it the level determined.

The propagation speed of the electromagnetic Signals and the distances between the electronics 13 and the Container bottom and between the receiving and Evaluation circuit 15 and the container bottom are either known anyway or can by simple Reference measurements can be obtained. With this data results the amount of the measured runtime reflective section of the float 11 above the Tank bottom and thus the fill level.

1, the float is 11th a flat hollow disk-shaped hollow body with a Center hole through which the conductor 7 is passed. The float 11 surrounds a cylindrical portion of the Head 7 on all sides. Between the float 11 and the Head 7 is an annular cylindrical gap, so that the Float 11 is freely movable along the conductor 7.

The section reflecting electromagnetic waves this float 11 is metallic or metallic coated lateral surface 17 of the hollow body. The Shell surface 17 faces the coupling 9 and runs perpendicular to an axis 21 of the conductor 7.

At one end of the conductor facing away from the coupling 9 7, a holder 19 is provided on which the float 11 rests when the liquid surface is below the bracket 19 is located. The bracket 19 is only represented schematically and consists e.g. in a vertical bolt extending to the axis 21 of the conductor 7, e.g. is screwed through the conductor 7 and two ends has at least as far on both sides of the Head 7 protrude that the float 11 by the Bracket 19 is held on the conductor 7.

2 is a second embodiment of a Level meter according to the invention shown. It differs from that shown in Fig. 1 Embodiment only in that another Float 11a and another bracket 19a provided are. The float 11a is a metallic or Metallic coated hollow body that is exactly like the one in Fig. 1 shown float 11 is cylindrical, the however, in contrast to that shown in Fig. 1 Float 11 is not flat, but in the axial direction has a height H, the dimension of which is the same Order of magnitude like an outer diameter D of Float 11a.

The bracket 19a consists of one facing away from the coupling End of the conductor 7 molded cylindrical Tail.

3, 4, 5 and 6 are further exemplary embodiments shown, which differ from the previous two only due to the respective design of the float 11b, 11c, Distinguish 11d and 11e. These level gauges can of course also with brackets, as in the exemplary embodiments in FIGS. 1 and 2 are shown.

In the embodiment of Fig. 3, the float 11b an annular cylindrical hollow body 23 from a Plastic, e.g. made of polytetrafluoroethylene (PTFE). The Partial surface reflecting electromagnetic signals one on a coupling-facing end face of the Hollow body 23 arranged annular disc-shaped metal plate 25. This embodiment has the advantage that a ring-shaped metal plate loosely on one simple swimmer can lie on. It is inexpensive and the assembly is simple and therefore requires only one little effort.

In the embodiment of FIG. 4, the float is 11c a solid ring cylinder made of a material with a high dielectric constant, that reflecting electromagnetic waves. Under a high Dielectric constant is a dielectric constant to understand, whose value is significantly larger than the value the dielectric constant of one over the product located medium. Typically located above of the medium air with a dielectric constant of 1. In connection with air, a material would have one Dielectric constant greater than 3 sufficient by one to get sufficiently high reflection coefficients.

Such swimmers have the advantage that they are homogeneous bodies. Since no connections are required the manufacture of such floats is very easy.

For applications where e.g. for mechanical reasons and / or chemical resistance a massive float from a material with a lower Dielectric constant can be used, like 5, a float 11d can be provided which has a solid base body 27 on the coupling-facing end face a thin layer 29 highly reflective of electromagnetic signals, e.g. a metallic coating, a thin metal plate or a conductive plastic layer is applied.

6 shows a further exemplary embodiment with a float 11e, in which a layer 31 reflecting electromagnetic signals is arranged between two partial bodies 33 of the float 11e. The partial body 33 can be both solid elements and hollow bodies. The layer 31 is, for example, a metallic coating of one of the partial bodies, a metal disk or a layer made of a conductive plastic.
The layer 31 is preferably arranged entirely in the interior of the float 11e.

This offers the advantage that the electromagnetic signals reflective section, here the disc 31, not with comes into contact with the product. So it is practical no risk of corrosion. The section can therefore be made be made of a simple and cheap material.

Preferably, the materials and dimensions of the individual components of the floats 11, 11a, 11b, 11c, 11d, 11e with regard to the specific density of the filling material selected that each of the reflecting sections have reflective surface with the Product surface lies in one plane and perpendicular to Axis 21 of the conductor 7 run.

In the float 11 of Fig. 1, this is the outer surface 17, in the float 11a of FIG. 2, this is one ring-shaped coupling-facing end face of the Hollow body, in the float 11b of Fig. 3, this is the Metal plate 25, in the float 11c of Fig. 4, this is a ring-shaped coupling-facing End face of the float 11c, in the float 11d from Fig. 5, this is the layer 29 and that of the swimmer 11e of FIG. 6, this is the reflective layer 31.

If the reflective sections are reflective Have area that with the product surface in one Level, the runtime measurement directly results in the correct level. Otherwise the distance should be between Product surface and reflection level determined and the Runtime measurement or the measured fill level accordingly Getting corrected.

Fig. 7 shows an embodiment of a block diagram the electronic circuit 13 and the receiving and Evaluation circuit 15.

The electronic circuit 13 has a transmit clock 50 and a transmission pulse generator 52. A transmission clock of the Transmit clock 50 is the transmit pulse generator 52 is fed. A transmit pulse generator is preferred 52 is used, which generates electromagnetic signals that the form of low energy high frequency short Have pulses. Such transmit pulse generators and in Connection with usable electronic circuits and Receive and evaluation circuits are e.g. in the USA 5,345,471 and US-A 5,361,070. They are pulses with a peak line of less than 1 µW and one effective power 1 nW or less with frequencies of 100 MHz and more can be generated. The send clock rate is e.g. a few MHz.

The electromagnetic signals are via the coupling 9 fed to the conductor 7. Conversely get along the Head 7 reflected signals via the conductor 7, the Coupling 9, the directional coupler 54 and one Directional coupler 54 downstream high pass 56 for receiving and Evaluation circuit 15.

The receiving and evaluating circuit 15 comprises one Time delay 58, at the input of which the transmission clock of Send clock generator 50 is present and the one sampling clock generated by a variable delay time delayed transmission clock corresponds. The variable Delay time is e.g. using a sawtooth generator provided. The sampling clock is one Sampling pulse generator 60 is supplied, which is dependent on Sampling clock generated sampling pulses and a first input a sample and hold circuit 62 supplies. Sampling and Transmit pulse generator 52, 60 are preferably identical, see above that the electromagnetic generated by them Signals only by the variable delay time differentiate.

The reflected signals are over the directional coupler 54 and high pass 56 at a second input of the sensing and Hold circuit 62 on.

In operation are preferably periodically with the Transmit clock frequency generates short transmit pulses and the reflected echo signals from the sample and hold circuit 62 fed. There, each echo signal becomes a sampling pulse superimposed and a resulting overall signal recorded by means of a downstream amplifier 64 amplified by means of one in series with amplifier 64 arranged analog-to-digital converter 66 digitized and fed to a microprocessor 68 as a sample.

The overall signal is a measure of the agreement of Echo signal and sampling pulse. The echo signals hit periodically one and successive sampling pulses differ from each other in that according to one Sawtooth function time delay. Under the Prerequisite that successive echo signal does not differ significantly, provides the sampling and Hold circuit 62 a stroboscopic record of the Echo signals. This requirement is typically always fulfilled, since the level in the period between two transmission pulses practically does not change.

The microprocessor 68 is connected via a first line 70 the transmit clock generator 50 and via a second line 72 connected to the sampling clock generator 58. Operational the microprocessor 68 regularly starts measuring cycles. While The electromagnetic signals become a measuring cycle periodically generated as previously described and the reflected signals sampled. A measuring cycle ends when all provided according to the sawtooth function Time delays were run through. It will be the individual samples in connection with the assigned current delay recorded. This gives a measurement signal curve from which the transit time is determinable.

8 shows two measurement signal curves of which a first measurement signal curve marked with a a level meter without a float and a second with b marked measurement signal curve with a Level measuring device with a float Polytetrafluoroethylene (PTFE), which is a coupling-facing Front surface coated with aluminum foil has been recorded. Both measurements were made with a medium with a low dielectric constant. It is the normalized samples against the Delay time recorded.

With short delay times, the measurement signal curves are a and b identical. The first maximum of the two Measurement signal curves a and b is due to reflections in the area the coupling 9, where inevitably jumps in impedance occur conditionally. The second maximum of the Measurement signal curve a is due to a reflection on the Due to the product surface, the second maximum of Measurement signal curve b is due to a reflection on the float attributed.

The amplitude of the second maximum of the measurement signal curve b is approximately three times the size of the second maximum of the Measurement signal curve a and the width of the reflection peak is the measurement signal curve b is significantly lower than that of Measurement signal curve a.

The accuracy with which the level can be determined depends much depends on how exactly the location of the second Maximum can be determined. The accuracy is all the more larger, the larger the amplitude of the maximum and the more the width of the associated reflection peak is smaller.

As clearly shown in Fig. 8, the measurement accuracy can by the use of a float according to the invention Products with low dielectric constants clearly be improved.

Claims (8)

Level measuring device for measuring a level of a liquid (1) in a container (3), which comprises an electronic circuit (13), - which generates electromagnetic signals during operation, a conductor (7), - which protrudes into the container (3), - along which a float (11, 11a, 11b, 11c, 11d, 11e) runs with the fill level, --- which has at least one section reflecting electromagnetic signals, a coupling (9), - Which transmits the signals from the circuit (13) to the conductor (7), --- which conductor (7) leads the signals into the container (3) and a signal reflected from the float (11), and a reception and evaluation circuit (15), - which receives the reflected signals, - which determines a transit time of the signals and - which determines the level from the runtime. Level measuring device according to claim 1, wherein the Float (11) a hollow body and that Section reflecting electromagnetic waves a metallic or metallic coated Shell surface (17) of the hollow body. Level measuring device according to claim 1, wherein the Section one inside the float (11e) arranged reflecting electromagnetic signals Area is. Level measuring device according to claim 1, wherein the Section a perpendicular to an axis (21) of the Conductor (7) extending electromagnetic signals reflective surface. Level measuring device according to claim 1, wherein the Float (11c) made of a material with a high Dielectric constant exists reflecting electromagnetic waves. Level measuring device according to claim 1, in which at one end of the conductor facing away from the coupling (9) (7) a holder (19, 19a) is provided on the the float (11, 11a) rests when the Liquid surface below the holder (19, 19a). Level measuring device according to claim 1, wherein the Float (11, 11a, 11b, 11c, 11d, 11e) one cylindrical section of the conductor (7) on all sides surrounds. Level measuring device according to one of the preceding Claims in which the reflective section is a has reflective surface with the Product surface lies in one plane.

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